Personally, all three of the motorized bikes I've built had only rear coaster brakes. Not the best set up, however, I do live waaaay out in the boonies and don't have a lot of riding where I couldn't just coast to a stop.
I realize a lot of you ride in the city or more congested areas where good brakes are more than just a good idea.
I'll be the first to admit I know nothing about bike brakes except the cable pull type and some of the variations of those, and coaster brakes.
I have had my coaster brake fail, coming down Mt. Lemon after the Death Race. The hub got hot and just stopped working, I had to jam my foot between the tire and seat post tube to stop. And you know what is really really bad? I still have not added front brakes! Shame on me
I consumed every set of brake pads that I bought at Wall-e-world almost immediately.
I found an abandoned bicycle with American made pads and two ell shaped support brackets that ride on the rear frame to align the pads properly.
These pads are still going strong.
I stripped the bike for everything usable after this.
I have regular old V brakes on my MB. I ran a new cable for the rear brake simply because my fuel tank was in the way of the factory setup. They can stop me dead in under the legal time for motorcycles here in NYS.
I was some what of an moron. I purchesed a bike that was set up for the size just bigger than the 26" alloys I knew I was going to get to make it more stable. Great part the sproket bolts right in, bad part smaller wheels means I can't use the breaks it came with. V brakes would be on the tires and not on the rims. when I swiched the front over to the alloy wheel I was able to bolt the disk brake right on to the wheel and the forks were set uo for both breaks. So right now I only have front breaks. Have never had touble with breaking too hard/fast to go over the handle bars or loose any control.
I ran a coaster brake when I first got into the scene and quickly relized that one brake wasn't enough. Since then I've changed my complete set up. I first had a 6 inch rotor on my bike and felt that wasn't enough stopping power. I now have an 8" rotor and it made a huge difference. That along with a V brake on the back finally put my mind to ease knowing I'll finally be able to stop when something jumps out in front of me. I recommend a disc brake for the front. It's the best way to go.
I had full discs on my full suspension MTB prior to motorization - I upped the front to a 203mm and kept the rear at 160mm. They are mechanical, BB7's with semi-metallic pads and SRAM full-metal-jacket cables. They bite hard at any speed, the cables give great feel and were simple to upgrade from stock.... just changed pads, front rotor and cables. Having ridden motorcycles for years, I know for myself, that I wouldn't be comfortable with anything less.... just my 2 cents